The present invention relates to gradient index optical fibers and more particularly, to an array of fibers forming an imaging lens array which transmits an image of an object plane to an image plane. In a preferred embodiment, the fiber and array parameters are optimized so that the same or better radiometric efficiency and uniformity are obtained while using fewer fibers than required in the prior art, thereby permitting construction of a lens array comprising a single row of gradient index fibers.
Image transmitters comprising bundled gradient index optical fibers are known in the art. U.S. Pat. No. 3,658,407 describes a light conducting fiber made of glass or synthetic resin which has a refractive index distribution in a cross section thereof that varies consecutively and parabolically outward from a center portion thereof. Each fiber acts as a focusing lens to transmit part of an image of an object placed at, or near, one end. An assembly of fibers, in a staggered two-row array, transmits and focuses a more complete image of the object. The fiber lenses are produced under the trade name "SELFOC"; the mark is registered in Japan and owned by Nippon Sheet Glass Co., Ltd.
These gradient index lens arrays have found use in a number of technologies; e.g. in construction of printed type electrical circuits as disclosed in U.S. Pat. No. 3,922,062 and as a replacement for conventional optical systems in copiers as disclosed in U.S. Pat. Nos. 3,947,106 and 3,977,777.
Because of the apparent optical characteristics of the gradient index fibers, it has heretofore been accepted that, to transmit images with acceptable image quality, a two row staggered array of fibers was required. The problems encountered with a one row configuration, were twofold: firstly, maintaining the two-row radiometric efficiency so that the particular image is transmitted at the required level of illumination and secondly, reducing the spatial modulation of the illumination to acceptable levels.